Anharmonicity in the Vibrational Spectra of Naphthalene and Naphthalene-d8: Experiment and Theory

In this paper, we report the gas phase infrared (IR) spectra of naphthalene and naphthalene-d(8) recorded in the mid infrared region (3200-500 cm(-1)) using a heated multipass long path gas cell. Several combination bands appear as shoulders and satellite peaks in the 3200-2600 cm(-1) region along with the C-H stretch fundamental bands. Experimental IR spectra of these molecules were systematically analyzed with vibrational self consistent field (VSCF) theory, vibrational second order perturbation theory (VPT2) and vibrational couple cluster method (VCCM) with two different potential energy surfaces obtained using B3LYP and MP2 methods. A comparative study between these two PESs was made to match the observed spectra. Final assignment of the IR spectra of naphthalene and naphthalene-d(8) was done the best match.